There was once was an operating systems that allowed you to format your entire hard drive when you only intended to format a floppy disk, if you typed format c: instead of format a:. This was called Microsoft Dos 2.x.
mkfs.vfat /dev/sda1
(At least, the man page for my mkfs.vfat doesn't include any options suggesting it protects against formatting already-formatted or mounted filesystems.)
Killed a windows install (which had the first partition on the disk) only a year ago with that one.
"Yes by all means, use a nonexistent file as input to overwrite an existing file That doesn't even have a .tar extension. That's exactly what I wanted"